The present invention relates to magnetic tape cassettes, and more particularly to a compact magnetic tape cassette which is substantially equal in size to a so-called Philips-type magnetic tape cassette.
Recently, cassette tape recorders have been reduced in both size and weight, and magnetic tape cassettes used in such recorders have been also miniaturized. Further, there has been a strong demand for provision of compact magnetic tape cassettes which are suitable for recording and reproducing signals with a high quality and at a high density and which have long playing times.
Heretofore, in the case of compact magnetic tape cassettes generally employed for audio usage, analog signals are utilized for recording and reproducing. In the analog system, recording and reproducing at a high density are necessarily limited. However, it is well known that employment of a digital system such as a pulse code modulation (PCM) system in which recording and reproducing operations are carried out with input signals converted into pulses makes it possible to perform high density recording and reproducing operations without noise induced in signal communication paths and without being affected by the quality of recording media.
On the other hand, recent research and development has provided a magnetic head which, using a multi-track recording technique, can perform high density recording and reproducing operations even with a magnetic tape used in the Philips-type magnetic tape cassette. As a result, multi-track recording and reproducing operations can be achieved with a compact magnetic tape cassette which is substantially equal in size to the standard Philips-type magnetic tape cassette.
It is assumed for multi-track recording using a stationary head system thirty-six tracks are used in both directions. In this case, the width of each track is of the order of 100 microns, which is much smaller than that for the conventional four-track recording operation with the Philips-type magnetic tape cassette. That is, the effective area of the magnetic head on each track is considerably small. Therefore, if dust is present in the space between the magnetic head and the magnetic tape, its adverse effects on the recording and reproducing characteristics are much greater than in the case of the conventional recording operation.
A typical example of a magnetic tape cassette presently used for high density recording and reproducing operations is a video tape cassette, which is recorded on and reproduced using a rotary head system. In order to protect the magnetic tape in the cassette from damage and to prevent harmful influence of dust on the high density recording and reproducing operation, the cassette is provided with a swingable guard panel on the front opening. In the case of the rotary head system, the magnetic tape is run only in one direction for recording and reproducing (except when a special type of tape cassette is used), and therefore the cassette case need not be of a symmetrical structure to permit the use of both sides (A and B) of the cassette. Furthermore, in the rotary head system, typically, two magnetic heads forming a predetermined angle with the tape running direction are alternately brought into sliding contact with the magnetic tape, thus removing dust from the magnetic tape. Accordingly, the adverse effects of dust on the recording and reproducing characteristics in the rotary head system are less than for a stationary head system.
A magnetic tape cassette to which the technical concept of the invention is to be applied employs a stationary head system, similar to the case of the Philips-type magnetic tape cassette, and has a number of recording tracks. Furthermore, in this magnetic tape cassette, both the upper and lower halves of the magnetic tape are used for recording and reproducing operations. Since the cassette is a one which has both A and B sides, and since the cassette is operated according to the stationary head system, as explained above, the recording and reproducing characteristics are more sensitive to the adverse effects of dust than a cassette operated with the rotary head system. Accordingly, the cassette should have a guard panel which provides a greater protection against dust than the guard panel of a video tape cassette.